The Green River is an 89 miles (143.2 km) tributary

Tributary

A tributary or affluent is a stream or river that flows into a main stem river or a lake. A tributary does not flow directly into a sea or ocean...

 of the Rock River in northwestern Illinois

Illinois

Illinois is the fifth-most populous state of the United States of America, and is often noted for being a microcosm of the entire country. With Chicago in the northeast, small industrial cities and great agricultural productivity in central and northern Illinois, and natural resources like coal,...

 in the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

. Via the Rock, it is part of the Mississippi River

Mississippi River

The Mississippi River is the largest river system in North America. Flowing entirely in the United States, this river rises in western Minnesota and meanders slowly southwards for to the Mississippi River Delta at the Gulf of Mexico. With its many tributaries, the Mississippi's watershed drains...

 watershed

Drainage basin

A drainage basin is an extent or an area of land where surface water from rain and melting snow or ice converges to a single point, usually the exit of the basin, where the waters join another waterbody, such as a river, lake, reservoir, estuary, wetland, sea, or ocean...

. Much of the Green's course has been straightened and channelized.

Course

The Green rises in northern Lee County and flows initially southwestward through Lee, Whiteside and Bureau

Bureau County, Illinois

Bureau County is a county located in the U.S. state of Illinois. According to the 2010 census, it has a population of 34,978, which is a decrease of 1.5% from 35,503 in 2000. Its county seat is Princeton. Bureau County is part of the Ottawa–Streator Micropolitan Statistical Area...

 Counties, passing the town of Amboy

Amboy, Illinois

Amboy is a city in Lee County, Illinois, along the Green River. The population was 2,561 at the 2000 census. The chain of Carson Pirie Scott & Co. began in Amboy when Samuel Carson opened his first dry goods store there in 1854...

. It turns westward in Bureau County and flows into Henry County

Henry County, Illinois

Henry County is a county located in the U.S. state of Illinois. According to the 2010 census, it has a population of 50,486, which is a decrease of 1.0% from 51,020 in 2000. Its county seat is Cambridge...

, where it roughly parallels the Hennepin Canal

Hennepin Canal

The Hennepin Canal Parkway State Park, also just called the Hennepin Canal, is an abandoned waterway in northwest Illinois, between the Mississippi River at Rock Island and the Illinois River near Hennepin. The entire canal is listed on the National Register of Historic Places.Opened in 1907, the...

 and passes the towns of Colona

Colona, Illinois

Colona is a city in Henry County, Illinois, along the Green River. It is part of the Quad Cities metropolitan area. The population was 5,099 at the 2010 census, down from 5,173 at the 2000 census....

 and Green Rock

Green Rock, Illinois

Green Rock is a neighborhood of the city of Colona in Henry County, Illinois, United States. Once a separate community, Green Rock was named so because it is the place where the Green River meets up with the Rock River....

. It joins the Rock River just west of Green Rock, in the Quad Cities

Quad Cities

The Quad Cities is a group of five cities straddling the Mississippi River on the Iowa–Illinois boundary. These cities, Davenport and Bettendorf and Rock Island, Moline, and East Moline , are the center of the Quad Cities Metropolitan Area, which, as of 2010, had an estimated population of...

 metropolitan area

United States metropolitan area

In the United States a metropolitan statistical area is a geographical region with a relatively high population density at its core and close economic ties throughout the area. Such regions are not legally incorporated as a city or town would be, nor are they legal administrative divisions like...

.